Quick-opening manway closure

ABSTRACT

A manway closure which provides a quick-opening entrance to a pressure vessel. The closure includes a domed cover which swings between open and closed positions with respect to a ring fixed to the vessel. The cover at its rim seats against an interior face of the ring and a sealing gasket is located between the cover rim and the interior face of the ring. The cover is constructed with respect to the ring so that when fluid pressure is applied internally of the assembly, the cover rim expands against the ring, compressing the gasket and thus forming a rupture-resistant seal.

llited ttes [191 ressler et a1.

]Marelr 26, 1973 QUICK-OPENING MANWAY CLUSU [75] Inventors: Marcus N. Bressler, Wilmington,

[58] Field of Search ..220/32, 34, 37, 46 R, 55.3, 220/55 R, 46 P, 24.5, 55 PC, 55 N, 55 AN; 16/147; 292/2566, 304

[56] References Cited UNITED STATES PATENTS 479,936 8/1892 Foster ..220/32 UX 1,326,124 12/1919 Vischer, Jr ..220/55 AN 2,355,475 8/1944 Skaller ..220/46 R 2,555,473 6/1951 Deaton 2,653,509 /1953 Nineberg ..220/34 X 2,726,006 12/1955 Brewer et a1 ..220/46 R X 2,839,218 6/1958 Zerbe 3,101,953 8/1963 Bosshard 3,387,738 6/1968 Kemp ..220/46 R 3,462,041 8/1969 Wilson ..220/46 R FOREIGN PATENTS OR APPLICATIONS [5 7 ABSTRACT A manway closure which provides a quick-opening entrance to a pressure vessel. The closure includes a domed cover which swings between open and closed positions with respect to a ring fixed to the vessel. The cover at its rim seats against an interior face of the ring and a sealing gasket is located between the cover rim and the interior face of the ring. The cover is constructed with respect to the ring so that when fluid pressure is applied internally of the assembly, the cover rim expands against the ring, compressing the gasket and thus forming a rupture-resistant seal.

15 Claims, 10 Drawing Figures PATENTEUmzoms 3, ,3

SHEET 1 OF 3 1 1'1 1 A lijliii 40 mvmrorzs /2 MARCUS N. BRESSLER NORMAN C. SEBELIST %W I PATENIEDmzo ms sum 3 OF '3 INX'HN'TORS MARCUS N. BRESSLER NORMAN C. SEBELIST QUICK-OPENING MANWAY CLOSURE The present invention relates to a closure for a manway adapted to be connected to a vessel, and especially a vessel which contains fluid under pressure.

Closures of various types are well known for closing and temporarily sealing the entrance to a vessel or other container whichwill be placed under considerable internal fluid pressure. Such closures may be used, for example, to close access openings to both large and small storage units through which a man may pass, or to close openings into which measuring or other instruments may on occasion be placed.

It is highly desirable that such closures in their closed position act as an effective seal to prohibit fluid leakage and to hold the seal without rupture under relatively high internal pressures. While these closures must be effective sealing agents, they yet must have the capability of being opened quickly and easily when the fluid pressure within the container is returned to normal, so that a man may pass into the entranceway or so that some other function may take place through the opening. The unsealing and opening of the closure should take place in a minimum amount of time with a minimum number of unfastening steps, imposing the least possible effort upon the workmen opening the closure. After the inspection by man or by instrument has taken place or other function has occurred, the closure must be capable of being resealed quickly and easily, and must be capable of reattaining its high pressure seal over a great number of repeated closure openings and closings.

While a number of closures have in the past been produced by industry, they are characteristically unnecessarily large and cumbersome, entail many working parts and require an excessive number of steps for opening and closing of the closure.

Accordingly, it is the primary object of the present invention to provide a quick-opening closure for vessels which retain fluid under pressure, which is simple in structure, economical in manufacture, and yet which permits simple and quick opening and sealing, time after time, without failure.

It is a further object of the present invention to provide a quick-opening closure of the character described in which as the internal fluid pressure within the vessel is increased, the seal which prevents fluid leakage is improved and enhanced.

It is another object of the present invention to provide a quick-opening closure of the character described which in one embodiment includes a number of circumferentially spaced hinges, each of which is readily disengageable whereby the cover can be pivoted between its open and closed position on anyone of such hinges.

Another characteristic of such closures which have been previously produced by industry is that they all depend upon gaskets placed under moderate compression to prevent fluid leakage. Thus, the sealing capability of prior closures ultimately depended upon the inherent ability of the gasket to resist its own rupture, for as soon as the gasket ruptured, the seal broke and the internal fluid pressure leaked. Another object therefore is to provide a sealing system which increasingly muzzles its gasket against rupture as the internal fluid pressure elevates.

In general, and in accordance with the teaching of the present invention, a quick-opening closure in a preferred embodiment is provided which includes a circular relatively rigid ring that is adapted to be fixed about an opening in any pressure vessel. The closure further includes a domed cover which is mounted by hinge means on the ring for movement between an open position and a closed position. A seat is formed in an interior wall of the ring, and the rim of the cover mates with the seat when the cover is in its closed position. The exterior face of the rim of the cover carries a gasket which is retained in a channel in the rim.

In this preferred embodiment, the domed cover is thin-walled as compared to the ring so that when the cover is closed and internal fluid pressure is applied within the closure, the cover expands relatively radially outwardly against the seat of the ring, and as it does so, the gasket is compressed between the seat and the rim. This increased compression of the gasket effects a seal which is highly resistant to rupture and leakage.

The hinge means in this preferred embodiment comprises a number of circumferentially spaced detachable hinges. This feature permits the cover to pivot on the ring on any one of the pivots, enabling opening of the cover on the ring at any one of several points on the ring circumference.

Other objects and features of the invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

FIG. I is a top plan view of the quick-opening manway closure in accordance with the present invention;

FIG. 2 is an elevational view of the manway closure and illustrating in broken lines the cover in its open position;

FIG. 3 is an enlarged fragmentary vertical cross-sectional view of the manway closure taken substantially along the line 3-3 of FIG. I;

FIG. 4 is an enlarged horizontal cross-sectional view of a first embodiment of the disengageable hinge means which is a component of the closure;

FIG. 5 is a fragmentary cross-sectional view of a second embodiment of the gasket-sealing means;

FIG. 6 is a fragmentary transverse cross-sectional view of a second embodiment of the disengageable hinge means;

FIG. 7 is a fragmentary longitudinal cross-sectional view of said hinge means taken substantially along the line 7-7 of FIG. 6;

FIG. 8 is a front perspective view of another e'rnbodiment of the closure, especially adapted to have its cover rotate about a vertical axis;

FIG. 9 is a fragmentary cross-sectional view of the lock means of the embodiment of FIG. 8, taken substantially along the line 9-9 of FIG. and

FIG. 10 is a fragmentary plan view of one lock unit of the hinge means of the embodiment of FIG. 8.

Referring now in detail to the drawings, and initially to FIGS. 1 through 3, the quick-opening closure 10 includes, as its basic components, a ring 12, a cover 14 and a number of circumferentially spaced hinge units 16. The cover is desirably domed.

The ring 12 is a heavy duty relatively rigid band of metal which is desirably substantially circular in plan. However, other obround and eliptical shapes would also be acceptable. The ring typically has a beveled lower edge 18 by which it is adapted to be fixed, as by welding, to any vessel, and especially any vessel which holds fluid under elevated pressures. The lower edge 18 of the ring 12 will be attached to the vessel so as to surround an opening or passageway in such vessel. Other known mechanical means may be used to attach the ring to the opening in a vessel.

A seat 20 (see FIG. 3) is formed in the ring 12 on an interior wall surface, and the seat 20 includes a generally vertical face 20a and a generally horizontal face 20b, these faces meeting at a corner 20c.

The cover 14 has a downwardly concave crown 22 which terminates in a lower rim 24. The rim has a generally vertical external face 24a and a generally horizontal face 24b, these orientations being taken when the cover is in its closed position. Desirably, the rim 24 is feathered outwardly so as to taper to a crosssectional width slightly less than the uniform cross-sectional width of the remainder of the cover 14. The configuration and external dimensions of the rim 24 match the configuration and internal dimensions of the seat 20. Hence, when the cover is in its closed position, the rim 24 fits nicely into the seat 20, with the vertical rim face 240 closely adjacent to the vertical face 20a of the seat and the horizontal rim face 24b abutting the horizontal face 20b of the seat.

The cross-sectional thickness of the cover 14 is, as shown schematically but not to scale in FIG. 3 of the drawings, considerably less than the cross-sectional thickness of the ring 12. The term cross-sectional thickness as used here means this dimension taken at an average location, typically, in FIG. 3, at xx on the cover 14 and y-y on the ring 12. That factor, taken with the domed configuration of the cover, enables the cover, and specifically the rim 24, to expand relatively radially outwardly under internal fluid pressure against the relatively rigid seat 20 of the ring 12, to thereby diminish any gap between the rim face 24a and the vertical face of the seat 20a. The term relatively is used since the ring wall 12 itself will expand outwardly under pressure; hence, for the proper operation of the manway closure, the cover rim must expand outwardly to a greater extent than the rim, for scaling to take place.

A sealing gasket is situated between the rim 24 and the ring seat 20, when the cover 14 is in its closed position. More specifically, as seen in FIG. 3, a radially outwardly opening channel 28 is formed in the rim 24, and a conventional O-ring gasket 30 is seated therein. The gasket 30 is compressed in the channel between the seat 20 and the rim 24, when the rim expands relatively outwardly to form a seal against the release of fluid pressure through the closure, as will be described more fully subsequently.

As shown in FIG. 5, the gasket may alternatively be situated in the ring. Specifically, the ring 12 has a radially-inwardly opening channel 28' formed on an internal wall, with the gasket 30' seated therein. When the rim 24 expands, it compresses the gasket 30 between the rim face and the ring, forming the desired seal.

The cover 14 is mounted to be swung between an open position (shown in broken lines in FIG. 2) and a closed position (shown in solid lines in FIG. 2) with respect to the ring 12. This mounting is effectuated by any one of a number of binge units 16. In a preferred embodiment of the present invention, four such hinge units 16 are utilized and these are equidistantly circumferentially spaced about the cover. However, a minimum of three hinge units may be utilized and more than four such units may also be utilized. A greater number of binge units are advantageously employed with larger diameter covers and to seal closures of the same diameter intended to accept higher internal pressures.

Each hinge has lugs 32 fixed to the cover 14 adjacent the rim 24. A tie bar 34 runs from one lug 32 to the other lug 32 of each hinge, for use as a handle, there being one such handle associated with each hinge unit for manipulation thereof by a user. The lugs 32, 32 have apertures 36 at their outer ends and these apertures are in alignment. Each hinge unit 16 further includes a sleeve 38 which is fixed as by welding to the ring 12 adjacent its upper edge. The sleeve 38 has a length such that it may fit between the pair of lugs 32 of its hinge unit. A headed pin 40 passes through the aperture in one lug 32, through the sleeve 38 and then through the aperture in the other lug 32, thereby to connect the lugs and the sleeve of a hinge unit for relative rotation. The pin can be readily slipped out of its position in a hinge unit by simply pulling the same out (when there is no pressure within the closure) and, by doing so, the members of a hinge unit are completely disengaged.

With the foregoing structure, each of the hinge units 16 is capable of functioning to enable rotation of the cover with respect to the ring. The user of the closure may selectively determine about which hinge unit the cover is to rotate by simply removing all of the pins 40 except the one in the hinge unit which is to act as the pivot. The hinge unit diametrically opposed to the unit selected to act as the pivot is grasped at the handle 34 and the cover is rotated to open the same. When the cover 14 is in its closed position, all of the pins 40 are placed in position in their respective hinge units to retain the cover on the ring.

A second embodiment 16 of the hinge unit is shown in FIG. 4 of the drawings. This embodiment includes, as described previously, a pair of lugs 32' fixed to the cover 14, a sleeve 38' fixed to the ring 12, the lugs 32 and the sleeve 38' having apertures which are in alignment. A pin 42 retains the sleeve 38 and the lugs 32 in an interconnected relationship. The pin 42 includes a protruding end 44 and an enlarged head 46. The end 44 has a through-aperture through which a cotter-pin 45 may be placed, to releasably retain the pin 42 in place.

The operation of the quick-opening closure may now be briefly described. When the cover is in its closed position, the lugs 32 and sleeve 38 of each hinge unit 16 are inter-connected by insertion of a pin 40 and the rim 24 of the cover mates with the ring seat 20. As the pressure of the fluid within the vessel and thus within the interior of the closure increases, the rim 24 expands relatively radially outwardly, because of its domed configuration and because it is thin-walled as compared to the thick, relatively rigid ring 12. As this expansion takes place, the vertical rim face 24a moves toward the vertical seat face 20a, first compressing the gasket 30 against the seat and after a certain degree of movement, face-to-face metal contact is attained. The foregoing gasket compression and face-to-face contact gives rise to a seal which is highly resistant to the passage of fluid under high pressure through the seal.

A third embodiment 16" of the hinge unit is shown in FIGS. 6 and 7 of the drawings. This embodiment includes a pair of lugs 32" fixed to the cover 14, a sleeve 38 fixed to the ring 12, the lugs 32" and the sleeve 38" having apertures which are in alignment, when the closure is non-pressurized. A pin 42" retains the sleeve 38" and the lugs 32" in an interconnected relationship. The pin 42" includes a protruding end 44" and an enlarged head 46' Further, the pin 42 includes a pair of spaced portions 47 of reduced diameter, the portions 47 being spaced apart to the same extent as the lugs 32" are spaced apart from one another. When the closure is under atmospheric pressure, the apertures in the lugs 32" and the aperture in the sleeve 38" are in exact alignment, permitting the pin 42" to be slipped in place or out of place freely. When the closure is pressurized internally, the cover 14 rises to a limited degree, causing the lugs 32" also to rise. Upon such movement, the bottom portions of the lugs 32" engage the portions 47 of the pin 42" of reduced diameter, thereupon prohibiting withdrawal of the pin 42". This arrangement acts as a safety feature, since whenever the closure assembly is pressurized, the pins 42" may not be withdrawn.

In a preferred embodiment of the present invention, the rim face 24a is machined to an extremely smooth distortion-free surface, and the mating face 200 of the seat 20 is similarly machined. Further, the rim face 24a is ground with a 5 to the vertical taper, while the face 20a of the seat 20 is ground with a 8 to the vertical taper. This vertical taper differential, in the range of 3, insures that the rim can swing into the seat without interference and without any scarring of the gasket, and the finish given to the mating faces 20a, 24a further insures a gap-free contact. It should be noted, however, that the vertical taper differential may be in the range 2 to 10 dependent on the respective tapers of faces a and 24a. Desirably, the aforesaid surfaces are given a 63 rms finish.

It should be appreciated that in closures of the same type previously known, a gasket was placed under moderate compression between a cover and a frame generally by mechanical means such as bolting. The gasket held its seal only to a level at which the fluid pressure was sufficient to force the gasket out of its intended position, usually into the fine gap between the cover and the frame, In the present structure, as the internal fluid pressure increases, the rim is forced with increasing intensity against the ring seat. As this happens, not only is the gasket compressed to a greater degree, but any gap between the opposed faces of the rim and the seat is materially reduced. In other words, the greater the internal fluid pressure, the greater the tendency of the closure to retain the gasket in place.

Tests have been made with the described closure to determine the maximum internal pressure which can be achieved before the seal will rupture, and these tests have proven the value of the closure design. A prototype closure was fabricated in which the cover consisted of an 18 inch standard ASME steel Flange and Dished Head having an 18 inch O.D. X inch wall, a ring made from a l /4 inch thick rolled and welded steel plate, 19 1% inch O.D. X 17 inch I.D., and three equally spaced hinge units. A conventional O-ring gasket was utilized, and the facing seat and rim faces were given a 63 rms finish. An internal pressure of psi was created, and it was noted that 0.060 inch of lift were measured at the center of the crown of the cover, with a return to 0.01 1 inch when the pressure was released. The prototype successfully withstood the 125 psi pressure.

Additional tests with the same prototype indicated that l50 psi pressure could also be sustained without rupture. Another test was run in which mild carbon steel bolts were substituted for the pins in the hinge units. At a pressure of 225 psi, the bolts were permanently bent into an open V shape, at which point the closure started to leak. The pressurization was stopped, and as the pressure dropped and reached 190 psi, the cover reseated and the pressure held at psi. Further tests were run with the use of hardened pins in the hinge unit, with the pins being 1 inch thick and the use of four equally spaced hinge units. The closure retained its seal at pressures at and above 300 psi.

In still another embodiment of the present invention, (not shown since the change therein involves primarily a different type of material as compared to previous embodiments), the cover 14 is made of a material with a lower Youngs Modulus of elasticity as compared to the material of the ring 12. Hence, when the fluid pressure within the closure is increased, the rim of the cover would expand outwardly faster than the ring so as to press the rim against the ring thereby to compress the gasket therebetween. In such an embodiment, typically, the cover could be formed of aluminum, and the ring formed of steel. The aluminum would be of a commercial grade while the steel would be of the mediumcarbon type. The cover would have an inside dimension of 17 inches and an outside dimension of 18 inches, while the steel ring would have an inside diameter of 18 inches and an outside diameter of 19 inches. Since the Youngs Modulus is lower for the aluminum cover than it is for the steel frame, and taking into account the above dimensions, the rim of the' cover would expand radially outwardly at a greater rate than the ring, causing the seal to be formed and maintained.

Another embodiment of the invention is constructed so that with an increase in the operating temperature of the unit, the seal is effected. In this form, the cover material must have a positive coefficient of expansion. Utilizing an aluminum cover and a steel ring, the coefficient of expansion of the cover is greater than the coefficient of expansion of the ring. It may be calculated that at an operating temperature of 200F., the cover will expand at a rate nearly twice the rate of expansion of the ring, thereby maintaining and enhancing the seal.

Another embodiment of the m'anway closure is shown in FIGS. 8 through 10. The primary advantage of this embodiment, as compared to the previous embodiments, is that the cover is set to be rotated about a vertical axis. It will be appreciated that this may have substantial advantage in particular installations. Referring now to said figures, the closure includes a tube 50 of relatively large diameter, which leads into or is a component of a pressure vessel. A ring 52 is fixed to the tube 50 by conventional mechanical means, as previously described. A domed cover 54 with a handle 56 centrally disposed thereon, is constructed and arranged to seat in, and by means of a gasket 58 seal with, the ring 52, substantially as previously described in connection with the embodiment shown in FIGS. 1 through 3. A hinge unit, generally 60, is provided to rotate the cover 54 with respect to the ring 52 and the tube 50, said cover being mounted for rotation about a vertical axis. The hinge unit 60 is a considerably heavier duty unit than similar units shown in FIGS. 1 through 7, since the hinge unit 60 must bear the entire unbalanced weight of the cover 54. Said hinge unit 60 includes a pair of legs 62, fixed to the tube 50, and which extend along the axis of the tube 50. A shaft 64 is journaled between the free ends of the arms 62, and a hinge plate 66 is fixed on one end to the shaft 64 and on the other end to the cover 54. The shaft 64 rotates about a vertical axis, permitting the cover 54 to rotate about the ring 52 and the tube 50 about a vertical axis. Locking means is provided to retain the cover 54 in its closed position and selectively to permit the cover 54 to be opened. Said means includes a band 68 which encircles the ring 52 and is rotatable within a channel 70 in said ring. A handle 72 is attached to the band at a convenient location so that, as will be seen, a user may shift the band 68 when it is desired to either lock or unlock the cover. The band 68 carries a number of spaced locking pins 74. The ring 52 carries a number of spaced sleeves 76, and the cover carries pairs of apertured arms 78 which straddle each sleeve. The sleeves 76 and the pins 74 are of the same curvature so that when the band 68 is shifted, the pins 74 are inserted into or withdrawn from the arms 78 and sleeves 76, interlocking them. In the inserted position, the cover is locked while in the withdrawn position, the cover is free to be swung open.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding 'use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

There is claimed:

1. A closure structure to provide an access opening for a pressure vessel comprising: a generally cylindrical ring adapted to be fixed about an opening in said pressure vessel, a cover having a generally concave crown terminating at its periphery to define a generally cylindrical rim extending axially away from the summit of said concave crown, means disposed on the outer surface of said cover and said ring for mounting the cover on the ring for movement between open and closed positions with the concave surface of the cover toward said access opening when the cover is in the closed position, the ring including a seat to receive the rim of the cover, a gasket situated between the seat and the cover rim when the cover is closed, the cover upon application of increased fluid pressure generally applied to the concave surface of the cover and internally of the closure expanding the cover relatively radially outwardly so as to compress the gasket between the rim and the ring.

2. A closure as set forth in claim 1 where the cover is thin-walled as compared to the ring.

3. A closure as set forth in claim 1 where the cover has a Youngs Modulus less than that of the rin 4. A closure as set forth in claim 1 wherein t e cover has a positive coefficient of expansion upon the application of increased temperatures.

5. A closure as set forth in claim 1 wherein the external face of the cover rim has a channel in which the gasket is retained.

6. A closure as set forth in claim 1 wherein the internal face of the ring seat has a channel in which the gasket is retained.

7. A manway closure as set forth in claim 2 wherein the cover rim is feathered to form a vertical taper differential with the opposed face of the seat.

8. A closure as set forth in claim 2 wherein the opposed walls of the cover rim and ring seat have a fine finish.

9. A closure as set forth in claim 1 wherein the mounting means comprise at least three disengageable hinge units spaced circumferentially around the cover, each hinge unit enabling pivoting of the cover on the ring at a different location on the ring.

10. A closure as set forth in claim 9 wherein each hinge unit includes a member fixed to the cover, a member fixed to the ring, and a pin detachably joining the members for relative pivotal movement.

11. A closure as set forth in claim 10 wherein means detachably retains each pin in its location connecting a pair of members.

12. A closure as set forth in claim 11 wherein said retaining means comprises a member situated transversely on the pin and removable therefrom.

13. A closure as set forth in claim 11 wherein said retaining means comprises portions of reduced diameter on said pin, segments of the member fixed to the cover protruding into said portions when the closure is under internal pressure.

14. A closure as set forth in claim 1 wherein locking means selectively joins the cover to the ring, said locking means comprising first locking members circumferentially fixed about the cover, second locking members fixed circumferentially about the ring, and means for selectively simultaneously interconnecting and disconnecting said first and said second locking members.

15. A closure as set forth in claim 14 wherein the mounting means is adapted to rotate about a vertical axis. 

1. A closure structure to provide an access opening for a pressure vessel comprising: a generally cylindrical ring adapted to be fixed about an opening in said pressure vessel, a cover having a generally concave crown terminating at its periphery to define a generally cylindrical rim extending axially away from the summit of said concave crown, means disposed on the outer surface of said cover and said ring for mounting the cover on the ring for movement between open and closed positions with the concave surface of the cover toward said access opening when the cover is in the closed position, the ring including a seat to receive the rim of the cover, a gasket situated between the seat and the cover rim when the cover is closed, the cover upon application of increased fluid pressure generally applied to the concave surface of the cover and internally of the closure expanding the cover relatively radially outwardly so as to compress the gasket between the rim and the ring.
 2. A closure as set forth in claim 1 where the cover is thin-walled as compared to the ring.
 3. A closure as set forth in claim 1 where the cover has a Young''s Modulus less than that of the ring.
 4. A closure as set forth in claim 1 wherein the cover has a positive coefficient of expansion upon the application of increased temperatures.
 5. A closure as set forth in claim 1 wherein the external face of the cover rim has a channel in which the gasket is retained.
 6. A closure as set forth in claim 1 wherein the internal face of the ring seat has a channel in which the gasket is retained.
 7. A manway closure as set forth in claim 2 wherein the cover rim is feathered to form a vertical taper differential with the opposed face of the seat.
 8. A closure as set forth in claim 2 wherein the opposed walls of the cover rim and ring seat have a fine finish.
 9. A closure as set forth in claim 1 wherein the mounting means comprise at least three disengageable hinge units spaced circumferentially around the cover, each hinge unit enabling pivoting of the cover on the ring at a different location on the ring.
 10. A closure as set forth in claim 9 wherein each hinge unit includes a member fixed to the cover, a member fixed to the ring, and a pin detachably joining the members for relative pivotal movement.
 11. A closure as set forth in claim 10 wherein means detachably retains each pin in its location connecting a pair of members.
 12. A closure as set forth in claim 11 wherein said retaining means comprises a member situated transversely on the pin and removable therefrom.
 13. A closure as set forth in claim 11 wherein said retaining means comprises portions of reduced diameter on said pin, segments of the member fixed to the cover protruding into said portions when the closure is under internal pressure.
 14. A closure as set forth in claim 1 wherein locking means selectively joins the cover to the ring, said locking means comprising first locking members circumferentially fixed about the cover, second locking members fixed circumferentially about the ring, and means for selectively simultaneously interconnecting and disconnecting said first and said second locking members.
 15. A closure as set forth in claim 14 wherein the mounting means is adapted to rotate about a vertical axis. 